Cardiac arrhythmias, atrial fibrillation in particular, persist as common and dangerous medical ailments, especially in the aging population. In patients with normal sinus rhythm, the heart, which is comprised of atrial, ventricular, and excitatory conduction tissue, is electrically excited to beat in a synchronous, patterned fashion. In patients with cardiac arrythmias, abnormal regions of cardiac tissue do not follow the synchronous beating cycle associated with normally conductive tissue as in patients with normal sinus rhythm. Instead, the abnormal regions of cardiac tissue aberrantly conduct to adjacent tissue, thereby disrupting the cardiac cycle into an asynchronous cardiac rhythm. Such abnormal conduction has been previously known to occur at various regions of the heart, such as, for example, in the region of the sinoatrial (SA) node, along the conduction pathways of the atrioventricular (AV) node and the Bundle of His, or in the cardiac muscle tissue forming the walls of the ventricular and atrial cardiac chambers.
Cardiac arrhythmias, including atrial arrhythmias, may be of a multiwavelet reentrant type, characterized by multiple asynchronous loops of electrical impulses that are scattered about the atrial chamber and are often self propagating. Alternatively, or in addition to the multiwavelet reentrant type, cardiac arrhythmias may also have a focal origin, such as when an isolated region of tissue in an atrium fires autonomously in a rapid, repetitive fashion. Ventricular tachycardia (V-tach or VT) is a tachycardia, or fast heart rhythm that originates in one of the ventricles of the heart. This is a potentially life-threatening arrhythmia because it may lead to ventricular fibrillation and sudden death.
One type of arrhythmia, atrial fibrillation, occurs when the normal electrical impulses generated by the sinoatrial node are overwhelmed by disorganized electrical impulses that originate in the atria and pulmonary veins causing irregular impulses to be conducted to the ventricles. An irregular heartbeat results and may last from minutes to weeks, or even years. Atrial fibrillation (AF) is often a chronic condition that leads to a small increase in the risk of death often due to strokes. Risk increases with age. Approximately 8% of people over 80 having some amount of AF. Atrial fibrillation is often asymptomatic and is not in itself generally life-threatening, but it may result in palpitations, weakness, fainting, chest pain and congestive heart failure. Stroke risk increases during AF because blood may pool and form clots in the poorly contracting atria and the left atrial appendage. The first line of treatment for AF is medication that either slows the heart rate or revert the heart rhythm back to normal. Additionally, persons with AF are often given anticoagulants to protect them from the risk of stroke. The use of such anticoagulants comes with its own risk of internal bleeding. In some patients, medication is not sufficient and their AF is deemed to be drug-refractory, i.e., untreatable with standard pharmacological interventions. Synchronized electrical cardioversion may also be used to convert AF to a normal heart rhythm. Alternatively, AF patients are treated by catheter ablation. Such ablation is not successful in all patients, however. Thus, there is a need to have an alternative treatment for such patients. Surgical ablation is one option but also has additional risks traditionally associated with surgery.
Diagnosis and treatment of cardiac arrhythmias include mapping the electrical properties of heart tissue, especially the endocardium and the heart volume, and selectively ablating cardiac tissue by application of energy. Such ablation can cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions. Various energy delivery modalities have been disclosed for forming lesions, and include use of microwave, laser and more commonly, radiofrequency energies to create conduction blocks along the cardiac tissue wall. In a two-step procedure—mapping followed by ablation—electrical activity at points within the heart is typically sensed and measured by advancing a catheter containing one or more electrical sensors (or electrodes) into the heart, and acquiring data at a multiplicity of points. These data are then utilized to select the endocardial target areas at which ablation is to be performed.
Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart of concern. A typical ablation procedure involves the insertion of a catheter having a tip electrode at its distal end into a heart chamber. A reference electrode is provided, generally taped to the skin of the patient or by means of a second catheter that is positioned in or near the heart. RF (radio frequency) current is applied to the tip electrode of the ablating catheter, and current flows through the media that surrounds it, i.e., blood and tissue, toward the reference electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to its electrical resistance. The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue which is electrically non-conductive.
Electrophysiology catheters also are often connected to electroanatomic mapping systems such as the Carto 3® system from Biosense Webster, Inc. Electroanatomic mapping systems are used in conjunction with mapping catheters to determine the anatomy of the endocardial tissue in the heart and where nerve fibers, nodes and bundles appear on that tissue which may be ablated to treat the aforementioned cardiac arrhythmias.
The handles of catheters for the mapping and ablation of cardiac tissue contain electronic circuitry which converts signals from the tip or ring electrodes near the distal end of the catheter into digital signals that can be communicated to the electroanatomic mapping system (such as the Carto 3® system from Biosense Webster) and/or an ablation system. The handles of these catheters must also be made so as to resist contamination from bodily and other fluids present during a procedure. Catheter handles are usually made of two matching halves that are laser welded together to create the final handle surrounding the printed circuit board (PCB) and other internal components. If there is a need to changes the PCB or other components in the handle a dental drill or saw is used to make a cut around the circumference of the handle to allow access to the interior. This can result in damage to the PCB, irrigation tubing or other components if not done with extreme care.
U.S. Pat. No. 7,189,228 to Eum discloses a detachable cryosurgical probe includes a disposable probe assembly and a reusable probe assembly. The disposable probe assembly includes a breakaway collar which, when twisted away, activates a finger lock element which provides release of the disposable probe assembly from the reusable probe assembly.
U.S. Pat. No. 6,496,228 to Rudie discloses a thermal therapy catheter for treatment of the prostate including a catheter shaft having an outer surface that is insertable into the body lumen The handle of the catheter is a two-piece, molded snap-fit shell according to an exemplary embodiment of the invention
U.S. Pat. No. 5,487,757 to Trukai discloses a multi-curve deflectable catheter having a handle with at least two detachable sections. A first detachable section including the structure for moving the stiffener wire and a second detachable section including the structure for applying force to the manipulator wire. A third detachable section could include structure for rotating the core wire. The detachable sections have universal connectors for connecting the detachable sections to each other. The universal connectors preferably comprise a snap fit adapter, wherein a male snap fitting on one detachable section engages a female snap fitting in another detachable section. In this embodiment, the catheter handle is modular, allowing various detachable sections to be selectively added or removed by the manufacturer depending upon the capabilities desired in the catheter, e.g. deflectability, rotatability, or stiffener control.
U.S. Pat. No. 5,242,430 to Arenas discloses a rotary handle for attachment to a proximal end of a catheter having components that “snap fit” together for ease of assembly.